This invention relates to a low profile pneumatic outlet for a covered hopper railway car or the like.
Typically, covered hopper cars are provided with pneumatic outlets to efficiently unload powdered, granular, or other pulverulent ladings from below in an expeditious and labor efficient manner. Hundreds, if not thousands, of pulverulent ladings have been transported by covered hopper cars and pneumatically unloaded utilizing prior art pneumatic outlet gates. In many service applications, such as in the transport of low density plastic pellets or other commodities, the limiting factor on the amount of lading a car can carry is determined by the volumetric capacity of the car rather than the weight of the lading. The Association of American Railroads (AAR) limits the total weight of a loaded rail car to 263,000 pounds. Typically, covered hopper rail cars of relatively large capacity weigh 60,000-65,000 when empty. This implies a maximum weight of lading carried on these cars of between 198,000-203,000 pounds. Since the weight of conventional covered hopper cars, when loaded, often are not up to the maximum AAR weight limit, it is beneficial to shippers to have a larger volume car such that more lading can be shipped on each trip of the car.
However, the AAR has also established a clearance diagram so rail cars can travel the rails safely without interference from trackside obstructions, bridges, tunnels or the like. Generally, these clearance diagrams limit the maximum width of the car to 10',8". The plate "C" AAR diagram, which is conventionally used for covered hopper railway car service, limits the maximum height of the car to 15'6" above the top of the rails. Also, the lowermost portion of the car body must be 2.75" above the top of the rails. All car appurtenances, such as walks, ladders, valves, railings, pneumatic outlets and the like must be kept within the boundaries of the clearance diagram.
The AAR has also defined a so-called base car and regulations which state, inter alia, that if the distance between the truck centers (i.e., the distance between the centers of the car trucks or wheel and axle assemblies) on a car are increased, the car must be made narrower to stay within the clearance diagram. For example, the base car defined by the AAR has a maximum width of 10'8" with the distance between truck centers being 41'3". If the distance between truck centers is increased to 75', the maximum width of the car must be decreased from 10'8" to 8'5". Thus, in designing covered hopper cars for a maximum lading carrying capability of low bulk density pulverulent materials, increased volume cannot be achieved merely by increasing the length of the car.
As previously noted, pneumatic outlets have long been used for unloading pulverulent materials from covered hopper cars. Reference is made to the co-assigned U.S. Pat. Nos. 3,701,460, 3,778,114, 4,114,785, 4,151,935, which disclose various pneumatic outlets in wide spread service which are commercially available from the assignee of this invention, ACF Industries, Incorporated, and which are identified by the ACF trade designations as 5131 and 5135 pneumatic outlets. Reference is also made to U.S. Pat. Nos. 3,048,448, 3,482,741, 3,876,261, 3,980,212, and 4,411,560 which disclose other pneumatic outlets.
All of these above-described prior art outlets may be characterized in that they are intended to be bolted to the bottom slope sheets of a railway hopper car and to have an elongate opening extending generally transversely of the car with the opening selectively opened or blocked by a valve. When the valve or gate is open, the pulverulent material within the railway car is free to fall downwardly into a generally transversely extending tube or air passage. This air passage is connected to an air conveying system which moves air rapidly through the tube so as to entrain the pulverulent material and to air convey the pulverulent material from the car.
Generally, the above identified prior art outlets utilize a rotary valve to control flow of pulverulent material into the air conveying tube located below the outlet.
Reference is further be made to U.S. Pat. Nos. 3,693,839, 3,693,846, 3,700,143, 4,388,026 and 4,695,207. These prior art patents disclose pneumatic outlets in which a single outlet gate is translationally (i.e., moved in horizontal direction without rotation) by means of a rack and pinion actuator or, in the case of the above-noted U.S. Pat. No. 4,695,207, by means of a crank mechanism.
While, generally, all of the above noted pneumatic outlets worked well for their intended purposes the prior art outlets were, relative to the present invention, tall from the bottom of their outlet tubes to the plane at which they were attached to the bottom of the hopper slope sheets. Since, in accordance with AAR regulations, the bottom of the outlet tube must be a prescribed height above the top of the rails, this defined the height of the bottom edges of the hopper slope sheets.
It is also necessary to provide a particular angle for the bottom slope sheets of the hoppers leading downwardly to the pneumatic outlets so to ensure that pulverulent material can be effectively unloaded by the pneumatic outlets. Thus, the height of the outlet and the required angle for the bottom slope sheets for the hopper and for the outlet pan defines the shape of the lower structure of the hopper car. This, in turn, defines the volume of the lower portion of the car.